1. Field of the Invention:
This invention relates to a film take-up spool for camera and, more particularly, to the shape of a flanged portion on the end of the drum of the spool.
3. Description of the Related Art:
The conventional film take-up spools for cameras have generally been known of the type in which the spool is provided with a claw for engagement with the perforations of the film to take up the film as the spool rotates.
FIG. 10 and FIG. 11 show an example of this conventional type of film take-up spool. A camera body 1 supports a film take-up spool 2 having a claw 2a in the vicinity of the lower end of a drum portion 2e thereof, around which the film F is wound with the perforation Fp in engagement with the claw 2a. A geared portion 2b in the upper end of the drum portion 2e is drivingly connected to an electric motor (not shown). Further, a flanged portion 2c for a film guide is formed beneath the geared portion 2b. Reference numeral 3 identifies is a flange for a film guide provided on the lower end of the drum portion 2e so as to confront the aforesaid flanged portion 2c in spaced relation, its diameter being slightly smaller than the inner diameter of a spool chamber 1b in the camera body 1. As shown in FIG. 11, the flange 3 which is near to the claw 2a is formed separately from the drum portion 2e. The reason why the flange 3 and the drum portion 2e are separately formed from each other is that if the flange 3 of the claw side is formed integrally with the drum portion 2e under the condition that, in FIG. 11, the outer diameter .phi..sub.B of the flange 3 is larger than the outer diameter .phi..sub.A of the flanged portion 2c, the flange 3 of the claw side could not pass through the spool insertion hole la formed in the camera body 1, because the spool insertion hole la is formed to the same size as the outer diameter .phi..sub.A of the flanged portion 2c. Thus, it would become impossible to assemble them. As its countermeasure, the inner diameter of the spool insertion hole la may be made equal to the outer diameter .phi..sub.B of the flange 3. But by the increase of the diameter of the spool insertion hole 1.sub.a, the rigidity of the camera body 1 would be very weakened, and the danger that light will leak through formed the gap between this spool insertion hole 1a and the flanged portion 2c. Accordingly, the possibility of the exposed film being fogged would very increase. For these reasons, it has been the common practice that the drum portion 2e and the flange 3 are separately formed from each other.
Nonetheless, the use of the separate form of the drum portion 2e ,and the flange 3 from each other in view of cost adds to cost of two parts. Also when assembling, the drum portion 2e is inserted past the spool insertion hole 1.sub.a, then the flange 3 of the claw side is put into the spool chamber 1b and then, while the drum 2e and the flange 3 of the claw 2a side are being brought into fitting engagement with each other in the interior of the camera housing, the drum portion 2e is fitted in a hole 1c of the lower side of the camera body 1. Such operations are very troublesome. Also, since the flanged portion 2c and the flange 3 of the claw 2a side are separate parts, the size control between both ends or the flanged portion 2c and the flange 3 is so difficult that there is a high possibility of not achieving the fundamental aim that the film is steadily held between these ends to prevent displacement of the film F to the thrust direction, or the so-called "bamboo shoots winding" phenomenon from occurring.
To restrain the film F from movement to the thrust direction by the flanged portion 2c and the flange 3, the first three or four turns of winding of the film must be controlled properly. And the subsequent turns will be wound up in the place. Conversely, if it happens that the first three or four turns are out of alignment in the thrust direction, the winding shift of the subsequent turns will grow, thus intensifying the above-mentioned "bamboo shoots winding" phenomenon.
Meanwhile, to eliminate the above-described problems of cost, assembling operations and size control, another spool has been proposed that, as shown in FIG. 12, a flanged portion 2d is formed at the claw 2a side also integrally with the drum portion 2e and its outer diameter .phi..sub.B ' is made equal to, or slightly smaller than, the outer diameter .phi..sub.A of the opposite flanged portion 2c to the claw 2a.
In other words, the use of the integral form of both flanged portions 2c and 2d with the drum portion 2e at the ends thereof makes it possible to reduce the cost. The assembling operation is only to put the spool 2 into the spool chamber from the above. Further, because all the portions of the spool 2 constitute only one part, control of the dimensions between both flanged portions becomes easy. As the shape of the tip of the film F varies, however, by using such a spool 2, an alternative problem arises.
That is, as shown in FIGS. 13(a) and 13(b), the tip of leader of the film F is, as typical examples, either outwardly rounded at the corners (hereinafter called "F type" (FIG. 13(a))), or inwardly rounded at the corners (hereinafter called "K type" (FIG. 13(b))). In the case when the film of K type is loaded to the spool 2, as shown in FIG. 12, because the outer diameter of the flanged portion 2d of the claw 2a side is small, it often happens that the tip of the leader of the film F rides on the outer periphery of this flanged portion 2d, as shown in FIG. 14. Even if the inside corner of the outer peripheral portion of this flanged portion 2d is tapered off to form a chamfer 2f, making it easier for the film F to slip down to the drum 2e side, the inward curvature of the cutout of the outside corner of the tip of the leader of the K type film causes this cutout portion to bite and ride on the outer peripheral portion of the flanged portion 2d. As a result, the perforation Fp of the film F is hindered from engaging with the claw 2a. Therefore, in the camera employing the auto-loading type windup mechanism, because, after the back cover (not shown) of the camera body 1 has been closed, the perforation Fp of film is engaged with the claw 2a and the film is wound up to a plurality of frames, a problem arises that winding up of the film becomes impossible.
Incidentally, in the case of using the F type film, even if the film rides on the flanged portion 2d, such a problem scarcely occurs because the convex curvature of the corners of the tip of the leader brings the tip down along the chamfer 2f to the drum portion 2e automatically or by the pressure of an auto-loading mechanism (not shown).